Okay, I've always felt that Front Squats were a great compound, quad dominant exercise, but I recently tried Hack Squats for the first time (about a month ago) and loved them.
For Hack Squats:
1) I felt much more fatigued in my quads after Hack Squats than Front Squats.
2) I was able to use much more weight with Hack Squats. Your body feels more weight, it will respond better as far as strength and muscle growth due to more hormone release.
3) Hack Squats are easier to get used to and require less time 'wasted' to learn the exercise (though once you learn it, there's no more time wasted).
For Front Squats:
1) Longer range of motion with Front Squats.
2) Any different exercise is good so your body feels something new.
That's all I could think up right now.
Does anyone see any reason to use Front Squats in place of Hack Squats?